The long-term objective of this proposal is to contribute to the understanding of the cellular basis of brain function and of processes controlling recovery of function following CNS injury or disease. The proposed research will be performed on three different levels including investigations of (1) modular organization of "functional units" in the intact mammalian corol in vivo; (2) microcircuits in cortical slices; (3) single dendritic spines. We propose to resolve biological questions that can significantly benefit from the unique capabilities of optical recording, a novel technology to the development of which the past research supported by this grant made a significant contribution. Optical recording is facilitated by the use of voltage-sensitive molecular probes. It supplies most of the information yielded by intracellular recording, but also has the unique and significant advantages: it permits recording from small neuronal elements; (2) mapping and imaging of activity is facilitated by recording from hundreds of loci simultaneously. Our specific aims are: (1) We shall employ the technology for real-time optical imaging of functional units in the frog optic tectum and the cortices of cats or monkeys in order to investigate their development, modular organization and interaction. (2) We shall implement optical and mathematical approaches which will permit tomography-like optical imaging of electrical activity with a unique temporal resolution in the submillisecond range and a three-dimensional spatial resolution of 30-60Mu. (3) The techniques will also be used to investigate microcircuits in the cortical slices and long-range interactions between functional units at a detailed level which could not be achieved with alternative methodologies. (4) The as yet undetermined electrical properties of dendritic spines will be investigated. The further development of the proposed technology will provide other neurophysiologists with a powerful tool to resolve many outstanding questions in neurophysiology, some of which have a direct medical significance. Its application to the investigation of demyelination diseases and epilepsy is described.